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Shikotsu-Tōya NP., Hokkaido
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Oshima’s deer boom began with 3 animals once kept for visitors: a stag and a doe escaped in 1957–58, and a pregnant doe was released in 1965. Their descendants eventually numbered about 450.
A volcanic dome near the northeast of Oshima’s four-island group has its summit just 1.5 m underwater. Formed about 50,000 years ago, it came close to becoming a fifth island—but never quite made it above the lake.
An Aka-ezo spruce on Oshima was selected among Japan’s “100 Forest Giants,” at 31 m tall with a 3.99 m girth. Typhoon No. 18 toppled it in September 2004; seedlings are now being raised.
Explorer Matsuura Takeshirō’s 1850s records preserve 2 Ainu names for Oshima: Tō-no-shike-moshiri, “island in the middle of the lake,” and Poro-shiri, “big island.” One island, 2 ways to describe it.
After eating down many preferred plants, Oshima’s deer switched to fallen leaves and even began eating creeping yew. The herd rebounded to 437 by 2003, then suffered another mass die-off in the winter of 2003–04.
A 2002–04 survey of the Nakajima islands found 150 plant species, just 32.6% of the 460 recorded in 1977. Herbs were hit especially hard: fewer than 1 in 5 of the earlier herb species remained.
Deer-proof plots on Oshima offer a hopeful contrast to the browsed forest: some plant species that had disappeared are appearing again inside the fences. The current coordinated management goal is to reduce the deer population to zero.
Oshima’s highest summit stands about 370 m above Lake Tōya, whose floor nearby lies roughly 175 m below the surface. From lakebed to summit, the mountain rises about 545 m—much more than its island silhouette suggests.
Oshima’s forest trail makes a 7.6 km circuit, taking about 3 hours through this uninhabited island. The route begins through a dedicated entrance inside the Lake Forest Museum, linking the exhibits to the forest outside.
